In computer science, particularly in programming, the term "Observable" refers to a concept commonly used in reactive programming. An Observable is a data structure or object representing a sequence of values or events that can occur over time.

Essentially, an Observable enables the asynchronous delivery of data or events, with observers reacting to this data by executing a function whenever a new value or event is emitted.

The concept of Observables is frequently utilized in various programming languages and frameworks, including JavaScript (with libraries like RxJS), Java (with the Reactive Streams API), and many others. Observables are particularly useful for situations where real-time data processing is required or when managing complex asynchronous operations.

Regular expressions, often abbreviated as "Regex," are sequences of characters that define a search pattern. They are primarily used in text processing to find, extract, or manipulate text patterns. Regular expressions provide a powerful and flexible way to search and manipulate text based on a specific pattern.

With regular expressions, you can, for example:

1. Search for text patterns: You can search for specific strings that match a defined pattern, such as email addresses, phone numbers, or URLs.

2. Extract text patterns: You can extract parts of a text that match a specific pattern, such as parsing data from a format.

3. Replace text patterns: You can replace text patterns in a text with other strings, such as substituting placeholders or removing unwanted characters.

Regular expressions are extremely flexible and allow the use of metacharacters and quantifying expressions to define complex patterns. They are supported in many programming languages and text editors and are a fundamental tool for text manipulation and analysis in software development, data processing, web development, and other fields.

LESS is a dynamic stylesheet language developed as an extension of CSS (Cascading Style Sheets). The name LESS stands for "Leaner Style Sheets," indicating that LESS provides additional features and syntactical improvements that make writing stylesheets more efficient and easier to read.

Some of the main features of LESS include:

1. Variables: LESS allows the use of variables to store values such as colors, fonts, and sizes and then use them at various places within the stylesheet. This greatly facilitates the maintenance and updating of stylesheets.

2. Nesting: LESS permits the nesting of CSS rules, improving code readability and reducing the need for repetition.

3. Mixins: Mixins are a way to define groups of CSS properties and then use them in different rules or selectors. This enables code modularization and increases reusability.

4. Functions and operations: LESS supports functions and operations, allowing for complex calculations or transformations to be applied to values.

LESS files are typically compiled into regular CSS files before being used in a webpage. There are various tools and libraries that can automate the compilation of LESS files and convert them into CSS.

Function-as-a-Service (FaaS) is a cloud computing model that allows developers to execute individual functions or code snippets without having to worry about the underlying infrastructure. Essentially, FaaS enables developers to upload and run code in the form of functions without dealing with the deployment, scaling, or management of server infrastructure.

The idea behind FaaS is that developers only need to write and upload the code that fulfills a specific function. The FaaS platform then handles the execution of this code when triggered by events or requests. A typical example of FaaS is using serverless computing in the cloud, where developers deploy functions in the cloud that run only when needed.

Popular FaaS platforms include AWS Lambda by Amazon Web Services, Azure Functions by Microsoft Azure, and Google Cloud Functions by Google. They allow developers to upload and execute code in various programming languages, simplifying application development and scalability without worrying about the underlying infrastructure.